This invention relates to an apparatus for performing music or a band selecting operation at high speed using a disk player.
Recently, a so called compact disc (CD) disk like recording medium has appeared commercially. On this disk program information, including address data, is helically recorded. Such a compact disk has the capability of storing recording music of about one hour duration on each side thereof. The music on each side may include about ten bands of music in the case of music of normal length; therefore, a for playing a compact disk must be able to select a desired band automatically and rapidly.
Accordingly, there has been proposed a band selecting apparatus as illustrated in FIG. 1. In reproducing music stored on a compact disk of this type, the distance to a desired band is obtained by address information with respect to the desired band and the address position with respect to a present or actual pick-up position. The pick-up is displaced in accordance with the thus obtained distance. In FIG. 1, the apparatus comprises a compact disk 1, a pick-up 2 for optically reading program information recorded on the compact disk 1, and, for converting the optically read out information, into an electric signal. An address data detecting section 3 detects address data from the electric signal obtained by the pick-out to thereby detect the present or actual position of the pick-up. A distance calculating section 4 calculates the number of tracks from the actual position of the pick-up obtained by the address data detecting section 3 to the address of a desired tune indicated together with a search instruction to thereby obtain the distance to the target. A counter 5 counts pulses produced by crossing tracks by the pick-up 2 when the pick-up 2 moves. A controller 6 controls the movement of the pick-up 2 to thereby perform the band selection. A pick-up displacement mechanism 7 displaces the pick-up in the radial direction of the compact disk, and an address judgment section 8 compares the actual address with the target address.
The technique of distance calculation performed by the distance calculation section 4 will now be described. The address information in the compact disk is expressed using the time from the starting point of the program information. One second is subdivided into 75 frames. The program information is recorded on the compact disk helically from a position on a 25 mm radius inner circumference of the disk to a position on a 58 mm radius outer circumference of the same disk with a constant linear velocity and with track pitch of 1.6 .mu.m.
The number of the frame F on a radius of r is expressed by the following equation (1): EQU F=(2.pi.r.times.75)/V (1)
where V represents the linear velocity of the disk.
If the pitch of track is represented by P, the following relation is satisfied: EQU r=P.times.n (2)
where n represents the number of tracks. Accordingly, EQU F=(2.pi..multidot.75.multidot.P.multidot.n)/V (3)
Accordingly, the total frame number (F.sub.total) from n.sub.1 to n.sub.2 is ##EQU1## Substituting the number T (=n.sub.2 -n.sub.1) of the tracks from n.sub.1 to n.sub.2 into the equation (3), ##EQU2## From the equation (5), ##EQU3##
Since the address information recorded on the disc from the position at a radius of 25 mm, the number of tracks from the position at a radius of 25 mm to the address can be obtained from the address information F by substituting the value r.sub.1 =25 into the equation (6). If the actual address and the target address are represented by F.sub.c and F.sub.a respectively, the distance .DELTA.T from the address F.sub.c to the address F.sub.a is as follows: ##EQU4##
The address will now be described. Upon reception of a band selecting instruction together with a target address, the controller 6 transfers the target address to the distance calculating section 4 to cause the distance calculating section to calculate the distance to the target address from the present or actual address of the pick-up 2 obtained by the address data detecting section 3. The controller 6 presets the result of the distance calculation in the crossing pulse counter 5 and at the same time produces a pick-up feed instruction to the pick-up displacement mechanism 7.
If the pick-up 2 is moved by the pick-up displacement mechanism 7, track crossing pulses are generated and counted downwardly by the counter 5. When overflow occurs in the counter 5, an output is applied from the counter 5 to the controller 6 which in turns produces a stop instruction to the pick-up displacement mechanism 7. The remaining distance to the target which could not have been attained by the above-mentioned pick-up feeding operation is handled as follows: the controller 6 determines the direction of further movement of the pick-up 2 on the basis of comparison between the present address and the target address effected by the address judgment 8; then, the controller 6 presets "200" in the counter 5 to cause the pick-up 2 to be moved by 200 tracks which correspond to one of several divisional parts of an average distance for one tune and produces a pick-up displacing instruction to the pick-up displacement mechanism 7. The pick-up feeding operation as described above is repeated until the output of the address judgment section 8 reverses, that is, until the address judgment section 8 judges that the target address has passed by the moving pick-up 2. Then, a further series of feeding operations are performed with a feeding pitch equal to one tenth of the previous one (that is, 20 tracks) for causing the pick-up to further approach the target address to thereby displace the pick-up 2 within a range of .+-.20 tracks.
FIG. 5 illustrated a flow chart of the technique of distance calculation performed by the distance calculation section 4. In the first step, the current address corresponding to the position of the pickup 2 is compared with the target address. If the current address is greater than the target address the pickup is moved in the reverse direction. If the current address is less than the target address then the pickup is moved in the forward direction. The number of tracks .DELTA.T in which the pickup is moved is determined in accordance to the formula, ##EQU5## The next step corresponds to the feeding operation in which the pickup is moved in accordance with the calculated distance. The counter is then preset with the number "200" corresponding to two hundred tracks. The pickup is then moved accordingly, and, a decision is made as to whether or not the distance moved is smaller than twenty tracks. If the distance moved is smaller than twenty tracks, the program ends. If the distance moved is greater than twenty tracks, the current address is then again compared to the target address. If the current address is greater than the target address, a decision must be made whether or not the displacement mechanism is currently feeding in the forward direction.
If the displacement mechanism is feeding in the forward direction then the direction is reversed and the counter is set to a value of twenty tracks. The feeding operation then continues and the pickup is moved 20 tracks. If the current address is greater than the target address, and the displacement mechanism is not feeding in the forward direction, then the feeding operation continues with the current value of the preset counter controlling the number of tracks moved. If the current address is less than the target address a decision must be made as to whether or not the displacement mechanism is feeding in the reverse direction. If the feeding mechanism is feeding in the reverse direction, then, the direction is reversed and the counter is set to twenty. The feeding operation then continues as the displacement mechanism moves the pickup in accordance with the value set in the counter.
A decision is again made whether or not the distance between the current address and the target address is smaller than twenty tracks. If it is, then, the controller 6 produces a stop instruction to the pick-up displacement mechanism 7. If the distance .DELTA.T is greater than twenty tracks, the foregoing procedure is repeated until the difference between the current address and the target address is less than twenty tracks.
Since the conventional band selector apparatus performs the operation in such a manner as described above, even if the necessary distance to the target address was calculated and the pick-up was rapidly displaced, it requires the repeated displacement of the pick-up by a certain quantity. Hence, this system can not execute a rapid band selecting operation. Further, since the moving and stopping operations are frequently repeated, there is a risk of deterioration in reliability in the pick-up and the pick-up displacing mechanism.
Thus, although the quantity of movement causes a problem in a search operation, the reason why it was necessary to perform such a large number of moves after the track searching operation had been performed while counting the number of tracks, was that it was impossible to accurately calculate the number of tracks to the target address. From equation (7), it can be determined that the number of tracks to a target depends on the linear velocity of a disk and the pitch of tracks. A disk standard defines the linear velocity to be 1.2 to 1.4 m/sec, and the track pitch to be 1.6 .mu.m.+-.0.1 .mu.m. However, the conventional tune selector apparatus does not have the ability for measuring the values of such a linear velocity and a track pitch. The calculation is performed by using values of a particular linear velocity and a particular track pitch suitably set within a standard range. Thus, it was impossible to avoid errors in pick-up displacing operations performed by using the result of such a calculation.